Codeigniter 3 - 加入并不返回所有结果

Question

我有这个问题：

return $this->db
        ->select('forumCategories.id, forumCategories.name, forumCategories.order, forumCategories.date_created, COUNT(forumPosts.forumCategory_id) as postCount')
        ->from('forumCategories')
        ->join('forumPosts', 'forumCategories.id = forumPosts.forumCategory_id', 'left')
        ->group_by('forumPosts.forumCategory_id')
        ->order_by('forumCategories.order DESC')
        ->get()
        ->result_array();

查询将获取所有论坛类别并计算每个类别的帖子。问题是它只采用有帖子的类别，而且只有一个类别没有任何帖子。

示例：

Category 1 | 16 posts
Category 2 | 3 posts
Category 3 | 0 posts
Category 4 | 0 posts
Category 5 | 0 posts
Category 6 | 0 posts

仅返回类别1,2和3。如何编写此查询，以便返回所有类别？

Answer 1

尝试使用始终具有值的第一个表列（forumCategories.id）进行分组。

 return $this->db
            ->select('forumCategories.id, forumCategories.name, forumCategories.order, forumCategories.date_created, COUNT(forumPosts.forumCategory_id) as postCount')
            ->from('forumCategories')
            ->join('forumPosts', 'forumCategories.id = forumPosts.forumCategory_id', 'left')
            ->group_by('forumCategories.id')
            ->order_by('forumCategories.order DESC')
            ->get()
            ->result_array();